Biomechanical comparison of pedicle screw fixation strength in synthetic bones: Effects of screw shape, core/thread profile and cement augmentation
Biomechanical comparison of pedicle screw fixation strength in synthetic bones: Effects of screw shape, core/thread profile and cement augmentation
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DOI：
10.1371/journal.pone.0229328
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发表时间：
2020-02-21
期刊：
影响因子：
3.7
通讯作者：
Tai, Ching-Lung
中科院分区：
文献类型：
--
作者：
Liu, Mu-Yi;Tsai, Tsung-Ting;Tai, Ching-Lung
骨-螺钉界面固定力不足导致椎弓根螺钉松动并不罕见。螺钉形状和螺纹牙型被认为是螺钉固定强度的重要因素。本研究探讨了三种不同螺纹设计的锥形螺钉和圆柱形螺钉在拔出强度上的差异。还评价了螺纹牙型对空心螺钉（有或无骨水泥增强）在骨质疏松骨中螺钉固定强度的影响。市售的人工标准L4椎骨和低密度聚氨酯泡沫块分别用作健康椎骨和骨质疏松骨的替代物。研究了9个螺钉系统的螺钉拔出强度（每个系统6个）。这些系统包括三种不同螺钉形状（实心/圆柱形、实心/圆锥形和空心/圆柱形）与三种不同螺纹轮廓（细螺纹、粗螺纹和双芯/双螺纹）的组合。实心螺钉设计用于使用标准样本进行椎骨的非骨水泥螺钉固定，而空心螺钉设计用于使用低密度测试块进行骨质疏松骨的骨水泥螺钉固定。在样本制备后，使用材料试验机进行螺钉拔出试验，并比较各组之间的最大螺钉拔出强度。这项研究表明，在健康椎骨中，锥形和双芯/双螺纹设计都可以提高拔出强度。锥形和双芯/双螺纹设计的组合可以实现最佳的术后螺钉稳定性。然而，在骨质疏松的骨中，当椎弓根螺钉固定时，骨水泥增强对螺钉固定强度的影响很小。与螺钉设计相比，骨水泥增强是影响螺钉拔出固定强度的最重要因素。
Pedicle screw loosening resulting from insufficient bone-screw interfacial holding power is not uncommon. The screw shape and thread profile are considered important factors of the screw fixation strength. This work investigated the difference in pullout strength between conical and cylindrical screws with three different thread designs. The effects of the thread profiles on the screw fixation strength of cannulated screws with or without cement augmentation in osteoporotic bone were also evaluated. Commercially available artificial standard L4 vertebrae and low-density polyurethane foam blocks were used as substitutes for healthy vertebrae and osteoporotic bones, respectively. The screw pullout strengths of nine screw systems were investigated (six in each). These systems included the combination of three different screw shapes (solid/cylindrical, solid/conical and cannulated/cylindrical) with three different thread profiles (fine-thread, coarse-thread and dual-core/dual-thread). Solid screws were designed for the cementless screw fixation of vertebrae using the standard samples, whereas cannulated screws were designed for the cemented screw fixation of osteoporotic bone using low-density test blocks. Following specimen preparation, a screw pullout test was conducted using a material test machine, and the maximal screw pullout strength was compared among the groups. This study demonstrated that, in healthy vertebrae, both the conical and dual-core/dual-thread designs can improve pullout strength. A combination of the conical and dual-core/dual-thread designs may achieve optimal postoperative screw stability. However, in osteoporotic bone, the thread profile have little impact on the screw fixation strength when pedicle screws are fixed with cement augmentation. Cement augmentation is the most important factor contributing to screw pullout fixation strength as compared to screw designs.